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About jwunderle

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    TT Newbie

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    trail riding, mountain biking
  1. jwunderle

    New OEM titanium valve - seat grinding / lapping

    First of all, 40 hours is way too low. You should get at least 200 hours from your Ti valves. Carefully inspect your air filter for dirt on the inside and brown residue around the intake. Use a clean paper towel for this. Granted Ti valves have their weakness in that when the coating wears off (my estimate is .005 in or 200 microns, the valve is shot and you will adjust it very frequently). What kills valves is dirt so pay attention to this first. If your valves don't leak gasoline or starting fluid after installation, you are good to go. Don't lap. If they leak, you need to dress the seats. This is a bit trickier and should be done by a machine shop unless the wear is very slight and a hand dresser may work. The higher forces associated with steel valves from the springs and inertia at high rpm's is a tradeoff. You could see cam or lifter wear due to this. If you are going to use high rpm frequently then the Ti valves are probably smart but for trail riding the SS valves have reportedly worked fine.
  2. jwunderle

    It's spreading!

    Its too bad someone doesn't make a lightweight (less than 180 lbs) affordable trail bike that is street legal and made for people who are of below average inseam length. This is possible but so far there has been too much emphasis on motocross like design which requires strength not needed for a mid-level trail bike. The Serow XT 225 was close but still too porky for many women to pick up if dropped.
  3. PS It occurs to me that part of jet engine required maintenance is to replace the main bearings. They do fail from fatigue eventually. Running low octane gas or sustained high speed operation could accelerate this failure and maybe the conn rod bearing is the weak link.
  4. My son rides the 426. He is 31 and is pretty fast. We spent a few days near Ridgecrest CA with quite a bit of high speed desert riding, maybe 200 miles mixed with a bit of hills and single track. On day 4 the bike stalled on a single track during normal riding. It felt very stiff to kick. Fortunately, he was able to get it started and ride to the highway where it quit again at high speed, locking the read wheel. Disassembly revealed that the lower conn rod bearing is very "stiff". I am wondering whether we should replace the crank bearings, too. It seems that there are a number of shops who will rebuild the crank including new rod and bearings for about $150. Anyone have thoughts on these choices. Thanks if you reply.
  5. jwunderle

    Yamaha WR250F 2001

    Fantastic bike, an XR250 on steroids.
  6. jwunderle

    Yamaha WR250F (2001)


    Fantastic bike, an XR250 on steroids.
  7. jwunderle

    I tried the trials tire and...

    Tried my new Pirelli MT-43 on the rear today at Carnegie SVRA. (For those of you who haven't read about this tire it has trials style tread and compound but has bias ply sidewalls and requires a tube) Conditions were 10% very slippery mud, 20% mud, 40% perfect and the rest pretty dry. Carnegie has some of the steepest longest climbs in California and a lot of really nasty treacherous user created trails. This tire does everything that others have stated. I was amazed. It hooks up as well or better than a knobby on all surfaces. What amazed me most was the directional control that I had on uphill turns or riding across the fall line. I tried it because it is much more trail friendly than knobbies but to my surprise its a way better tire for trail riding. I took it on the motocross track as well. I didn't feel any of the back end looseness that trials tires are supporsed to exhibit, likely due to the heavier bias ply sidewalls. DOT approved as well. If you want to do something to save the trails and be a more capable rider, I would suggest going to one of these for your next back tire.
  8. For those who make the same mistake that I did here is the solution. The engine side plate on the slide was upside down. If you put it back together so that the plate matches the slide, it will go back together and run but with the idle problems described above. The way to check its orientation is that the M on the plate should be right side up with the carburetor in the right side up position. I did notice that the wear marks didn't make sense but didn't take the time to figure it out because the shape of the slide and the plate are similar but opposite when installed correctly.
  9. Thanks for the tip. I changed the pilot jet but the bike still runs the same. I went to a 45 (because that's all they had) from a 42 and it seemed a little better but still surges. It does run OK with the cold start engaged which leads me to believe that there is something blocking the pilot circuit. I took out the pilot jet again and removed the pilot screw and ran a brush bristle through the hole. It was clear to the Venturi. I can't see what is in between the pilot jet and the pilot screw though. I will look to try to find a pilot circuit diagram somewhere. Thanks again.
  10. I recently changed the needle from position 3 to 4 because the power felt a little low in the middle. Other than that the bike ran fine. When I started the bike it wouldn't idle and the rpms were very irregular at low throttle position. The bike surges then dies. Once the throttle is opened about 1/8 turn things smooth out. I also get frequent pinging sounds, like small backfires during deceleration. From what I have read the symptoms sound like an air leak. I have had the carb apart several times and have not seen anything out of place. One area of suspicion is that I have a Dr D Hot Start assmebly with the button on the handlebars. The cable connection to the fitting on the carb seems very loose. In addition, the last time that I had the carb off, I noticed some dirt on the underside of the slide cover right in the middle. I have not seen this before. I have run the pilot jet adjustment in to 1 turn and out to 4 and there is not much difference. Any suggestions would be greatly appreciated.